The present invention relates to proximity probes, and, more particularly, to a method and apparatus for an injection molded eddy current probe attachment to a metal component without using mechanical fasteners or adhesives.
Monitoring and diagnosing the status of rotating and reciprocating machinery start with accurate and dependable measurements from a transducer and its associated electronics and then proceed to other sophisticated analyzing apparatus for reduction and display. One such transducer is a proximity transducer which may be utilized for, inter alia, monitoring the vibration characteristics of a rotating shaft of a machine. In this environment, the transducer must operate under very adverse physical, chemical and mechanical conditions and it is often very difficult to replace such transducers. Thus, there is an ongoing effort to make the proximity transducer one of the most reliable parts of the monitoring system.
Typically, the proximity transducer, in conjunction with associated electronics, outputs a signal correlative to the spacing between an object or “target” (the rotating shaft of the machine) and a sensing coil of the proximity transducer. It is critical that the length or spacing between the target and the sensing coil of the proximity transducer remains within the linear range of the transducer for providing accurate and reliable measurements when in operation. Thus, one hallmark for providing accurate and reliable measurements relies on providing a transducer which is impervious to the predations of the environment and which does not consume an inordinate amount of the linear range of the transducer.
Standard eddy current probe designs are typically a forward mount design with a probe tip in-line with an extension cable. However, an in-line, forward mount tip does not allow the probe to be mounted in extremely tight locations such as in-between critical machine components and a target surface being measured.
Probes designed for limited space mounting applications are very specific to each application, and currently involve a number of labor intensive, manually operated processes to manufacture them. For example, a typical right angle or small, limited space mounting probe includes hand machined non-conductive components for the tip, a hand wound sensing coil, and a hand mixed, manually applied epoxy to encapsulate the tip for attachment to a stainless steel probe case. The probe case is used to operably mount the tip to the machine.
However, it is a challenge to attach fiberglass or plastic components to metallic components without the use of mechanical fasteners. In addition, adhesives often fail to bond metal to some plastics or metals and simply molding plastic against a metal surface does not result in a robust engagement. For a permanent assembly, alternative means must be employed.
One such methodology implemented by the assignee of the present application employs cross drilled holes in a cylindrical metal component. Plastic is then injected in the voids between the metal and plastic components, including the cross drilled holes, to provide a juncture that attempts to secure both axially and torsionally.
However, this methodology does not provide a suitable volume of plastic to secure the cylindrical metal component with the plastic component. Furthermore, this methodology may not be feasible when, for example, a mold shutoff area on the metallic component is limited or when using plastic components having a different geometry.